Dispersion-hardened metal sheet and process for making same



United States Patent Ofice Patented June 11, 1968 3,388,010 DISPERSION-HARDENED METAL SHEET AND PRGCESS FOR MAKING SAME Robert E. Stuart, Christiana Hundred, DeL, and Roger E. Wiison, Baitimore, Md assignors, by mesne assignments, to Fansteel Metallurgical Corporation, a corporation of New York No Drawing. Filed July 29, 1965, Ser. No. 475,869 Claims. (Cl. 148-11.5)

This invention relates to processes for producing dispersion-hardened metals in the from of sheet having excellent ductility at room temperature and excellent elevated temperature strength and oxidation ressitance, and to the products so produced. More particularly the invention is directed to such processes wherein a powder comprised of nickel and from 10 to 30% of chromium by weight, said metals having prevasively dispersed therein particles of a refractory metal oxide having a free energy of formation at 1000 C. greater than 100 kilocalories per gram atom of oxygen, said particles having an average size less than about 80 miliimicrons and being present in the proportion of 0.1 to 6% by volume in the metals, is consolidated to plate form at a temperature below about 2200 F., the novel processes comprising the steps of (1) rolling said plate predominantly in one direction at a temperature of about from 800 F., preferably 1100 F., to 100 F. below its recrystallization temperature, said rolling being sufiicient to effect at least a 50% reduction in the thickness of the plate, and (2) thereafter heating said rolled product to a temperature and for a time suflicient to totally recrystallize the metal therein. The invention is further particularly directed to dispersion-hardened nickelchromium sheet which can be produced by the novel processes, said sheet comprising nickel and about from 10 to 30% by weight of chromium, said metal having pervasively dispersed therein about from 0.1 to 6% by volume of particles of a refractory metal oxide having a free energy of formation at 1000 C. greater than about 100 kilocalories per gram atom of oxygen and an average particle size less than about 80 millimicrons, said product being in the form of sheet characterized by excellent room temperature, ductility and high temperature strength and oxidation resistance and by having a grain structure characterized by the presence of a substantial proportion of grains with a length-to-thickness ratio greater than about 2 and a grain thickness in the range of about from to 200 microns.

In preferred processes and products of the invention the alloy consists essentially of nickel and about 15 to preferably about 20%, of chromium and the dispersed refractory oxide is thoria in the proportion of l to 4%, preferably about 2%, by volume, and having a particle size less than about millimicrons, preferably about 10 to 40 millimicrons. In one preferred aspect of the novel processes the consolidated plate is rolled, predominantly (at least 75%) in one direction and at a temperature of about from 800 F., preferably 1100 F, to 100 F. below its recrystallization temperature, to effect at least a reduction in thickness, the rolled product is formed to a desired shape, and thereafter the formed product is heated to a temperature and for a time sufficient to totally recrystallize the metal. One preferred sheet product of the invention is characterized by having a cubically aligned preferred orientation, said orientation being described with Miller indicies as (100) 001 It is already known that sheet products having excellent service characteristics at elevated temperatures can be produced 'by powder metallurgy techniques employing nickel dispersion-hadrened by such refractory oxides as thoria. However, in the fabrication of dispersion-hardened nickel-chromium alloys into the from of sheet by conventiional hotor cold-rolling methods the products have not possessed the desired high temperature strength in combination with useful room temperature dutility.

Now according to the present inventiion, it has been found that if a consolidated metal plate, containing a dispersed refractory oxide such as thoria, is rolled into sheet under controlled temperature conditions, and the sheet is thereafter heated at a temperature high enough to effect recrystallization of the metal therein, the sheet products obained have the desired room temperature ductility as well as the necessary elevated temperature strength and oxidation resistance. Furthermore, the room and elevated temperature yield and ultimate tensile strengths and room temperature ductility of the novel sheet products of this invention remain substantially unchanged after exposure in air to temperatures of 2400 F. for 100 hours.

In the products of the invention, the thoria or other refractory oxide is pervasively dispersed in the metal product. By this is meant that the thoria or other oxide is present in the grains as well as at the grain boundaries and. is not so agglomerated as to cause large areas of aggregates of the refractory metal oxide to be present in any particular part of the product.

It will be noted that the novel compositions of this invention are characterized by having a particular type of grain structure. Since the products have been recrystallized, their grain structure follows from that of the metal before such recrystallization and is critically related to the manner of rolling the product from consolidated form to the form of sheet. Thus the product in the process is rolled within critically controlled temperature limits until the grain structure is textured and contains grains which are longer than they are thick. In referring to grain structure it will be understood that the length is taken as the maximum dimension of the grain and the thickness as the minimum dimension. The degree of elongation in a particular grain can be then expressed as the ratio of the length to the thickness, the higher this ratio, the greater being the elongation. Upon recrystallization, the grains become substantially larger but they are still elongated, the ratio of length to thickness being at least about 2:1.

The chemical composition of the starting alloys and the size of the dispersed thoria particles have a pronounced influence on the process employed to obtain the products of this invention. Generally speaking, as the chromium content is lowered from 30 to 10% the recrystallization temperature is increased. In nickel alloys containing 2 volume percent thoria (20 m average size) sheets rolled 85% at about 1300" F. the recrystallization temperature is: 1450 F. for 20% Cr, 1625 F. for 15% Cr, and 1900 F. for 10% Cr. Similarly, if the thoria content is varied in the 20% Cr alloy from 2 volume percent to either 0.6 or 4.6%, the recrystallization temperature is found to change to 1250 F. for the 0.6% ThO and l950 F. for the 4.6% ThO alloy.

As the recrystallization temperature is altered by changes in the chromium content and thoria spacing the grain size of the recrystallized structure will also change provided the processing sequence or stored energy is held relatively constant. In the above-mentioned 0.6% thoria alloy the recrystallized grain size was small (about 5 1. thick), due to the low recrystallization temperature, whereas in the 4.6% thoria alloy the grain size was large (about thick).

For improved high temperature strength in dispersionmodified nickel-chromium alloys it is desirable to have a relatively coarse-grained structure, but for good room temperature ductility it is desirable to have a fine-grained structurepreferably a fine-grained, cubic-textured structure. For maximum high temperature strength a coarse grain structure is preferred. To get an optimum balance of both high strength at high temperature and satisfactory ductility at room temperature the grain thickness in a product of this invention is controlled at above about microns, preferably in the range of 15 to 200 microns, and still more preferably to 60 microns.

To measure the grain size of products of the invention conventional metallographic techniques are used. Certain etchants will reveal the presence of twins to a greater extent than grain boundaries, whereas for other etchants the reverse is true. In the dispersion-hardened alloys the twins often do not extend completely across the grains. Twins can be recognized by geometry relationships they bear to each other and can thereby be distinguished from the overall grain structure.

The development of a preferred orientation in the recrystallized sheet is dependent of the rolling process, which generates a preferred deformation texture. For instance, an alloy of Ni-20% Cr-Z vol. percent ThO (average Th0 particle size about 20 millirnicrons) when rolled predominantly in one direction to effect a reduction in thickness of more than 50% at 1300 F, will recrystallize to the cube texture; moreover if such an alloy is rolled to the same thickness reduction, but with half the rolling in one direction and half at a 90 angle thereto, it does not recrystallize to a cube texture. Accordingly, in a preferred process of the invention the rolling is carried out predominantly in one direction, preferably at least 75% of the total rolling being done in one direction.

Broadly stated, in a process of the invention one starts with a powder comprising nickel and from 10 to by weight of chromium, the metal phase having pervasively dispersed therein about from 0.1 to 6% by volume, preferably 1 to 4%, of a suitable refractory oxide having an average particle size less than about 80 millimicrons. The refractory oxide must have a free energy of formation at 1000 C. greater than 100 kilocalories per gram atom of oxygen, and preferably greater than 106 kilocalories. containing, such a powder saynicl el, 20% Cr and 2 volume percent thoria, can be prepared, for instance, by coprecipitating the hydrous oxides of nickel and chromium together with colloidal thoria of suitable size, drying the coprecipitate, and reducing the nickel and chromium oxides to the corresponding metals with hydrogen and finely divided carbon at a temperature of from 850 to 950 C.

The oxide-modified metal powder is then compacted, sintered, and hot worked at a temperature below 2200 F. into a coherent, consolidated plate having substantially theoretical density. The hot work can be conducted by such methods as forging or extrusion. It will be understood that these processes can be carried out as closely connected steps of a single operation, as when one extrudes a compacted powder billet directly into the shape of a ribbon or sheet-bar.

The plate so obtained is rolled to sheet, predominantly in one direction and at a temperature of about from 800 F. to 100 F. below its recrystallization temperature. In the early stages of the rolling step, plate having a recrystallization temperature of 1600 to 1900 F. and above can advantageously be substantially reduced in thickness at a temperature of 1500 to 1800 F., the temperature in any event being low enough to avoid recrystallization. In this way substantial economies are achieved, because at these relatively high temperatures a number of passes through the rolling mill can be effected before it is necesary to reheat the work piece.

Irrespective of the manner of preparing the consolidated body in the form of a material suitable for working to the final gauge sheet, the final rolling to the ultimate dimensions is also effected at a temperature in the range of about from 800 F., preferably 1100 F., to a maximum temperature which is 100 F. below the recrystallization temperature of the sheet at that state of processing. If extensive rolling is attempted at a temperature below about 800 F. cracking of the sheet may be encountered due to rapid work-hardening of the alloy and its reduced ductility and high hardness under these conditions. llf, on the other hand, temperatures above about 100 below the recrystallization temperature are used, incident recrystallization may occur in part or all of the sheet, and with this recrystallization a loss of ductility is encountered. An increase in strength is also encountered, and this merely adds to the problem of further rolling.

It is advantageous to maintain the fine grain structure throughout the process until the final recrystallization step. The original consolidated work piece is fine-grained, and even though the grains are changing shape, they remain small throughout the entire metallurgical working sequence. By the designated control of temperature during rolling, advantage is taken of the minimum strengths and maximum ductilities at these temperatures.

The final step of the processnamely, recrystallization, comprises heating the rolled sheet to a temperature above its recrystallization temperature and maintaining such temperature until substantially complete recrystallization has occurred. After recrystallization the maximum strengths and minimum ductilities are found at the abovedesignated and higher (to 2400 F.) working temperatures. Thus the process accomplishes the Working under conditions best suited to produce the desired products. If desired, the recrystallized sheet can be given final finishing treatment, such as cold-rolling up to a 20% reduction in thickness to provide good gauge control and flatness.

It is necessary to keep the thoria particle size relatively small in the sheet product to maintain maximum creep resistance and stability of the structure. The size must be below about millimicrons, preferably below 40 millimicrons and still more preferably should be in the range from l0 to 25 millimicrons.

The measurement of particle size of the dispersed refractory oxide such as thoria in these products can be made by several techniques, each of which offers different combinations of precision, validity, range, and ease of operability. A B.E.T. specific surface area measurement can be made of the residues extracted from the metal sample by bromine-methanol solution and this surface area converted to average diameter by assuming the particles are spherical. This method has the advantage of employing relatively large samples, but the results can be clouded by, for example, high surface area phases which along with the thoria are insoluble in the Br-rnethanol extraction medium.

A second method employs the measurement of X-ray line breadth, which is a standard method for small particles of crystalline substances. Here the problem area for thoria particles is loss of precision at approximately be low 15 m and above 80 mn. This method is generally satisfactory for powder samples of Ni-20 Cr-20 ThO but because of factors of preferred orientation, absorption characteristics, etc., the method is less satisfactory for consolidated samples (sheet) of the same alloy or samples containing small amounts of thoria or for samples whose dispersoids have weaker diffraction lines, such as A1 0 The method is specific to the dispersoid phase and can be operated so that the results are not clouded by the presence of other phases.

Other methods relying on electron miscroscopy can also be employed for thoria size measurement. Particles of thoria down to 10 my. and even less, projecting above the polished surface of a metallographic sample, can be repli cated, viewed, and measured on electron photomicrographs. Non-dispersoid particles can be distinguished from the dispersoid if their morphology is different. Similarly an extraction residue from a sample (used in the B.E.T. method) can be dispersed on a carbon substrate and the particle size determined by means of electron photomicrographs. Again, foreign phases (those which are not the dispersoid) can be avoided in the average size measurement only if their morphology is different. Transmission electron microscopy can also be used to measure dispersoid size, particularly in the case of thoria because of its high absorption characteristics, but this method tends to overlook or underemphasize the larger particles. The size measurements involving electron microscopy are often time consuming and in addition can be, although they may not necessarily be, biased because of the small volume of sample analyzed.

In samples of Ni-20 Cr-2 Tho of the present invention, X-ray line breadth and B.E.T. measurements have been employed for thoria size, and it has been found that the X-ray measurements yield a size number about mn larger than the B.E.T. method when the size is about mg (B.E.T.). These samples contained less than 100 ppm. C, N, S, and less than 1000 ppm. 0 as measured by vacuum fusion. Electron photomicrographs of replicas from such a sample reveal that virtually all (99%) of the dispersoid particles are below 8011111., and the average size, although not precisely measured by particle-counting techniques, appears by that method to be consistent with the X-ray and B.E.T. measurement Particle sizes referred to in this application are the BET. values unless otherwise specified.

The novel metal products produced according to the process of the invention have the following desirable properties:

(l) They are oxidation-resistant at high temperature. The nickel-20% chromium-2 vol. percent thoria sheet, for example, can withstand hundreds of hours of cyclic oxidation exposure to temperatures of 2200 F. with a weight grain of less than 10 mg./cm. This performance is better than any commercially available superalloy.

(2) They exhibit high strength at high temperature. At 2000 F. a sheet of nickel-20% chromium-2 vol. percent thoria can withstand a stress of 5,500 psi for more than 20 hours. Generally speaking, the sheet of this invention is at least twice as strong at 2000 F. as com mercially available superalloy sheet.

(3) The sheet of this invention is ductile, i.e., it can be bent without cracking, at least 90 at room temperature around a mandrel whose radius is 1 to 2 times the thickness of the specimen. Thus, it can be bent and formed at about room temperature into hardware requiring the oxidation resistance and strength developed by the dispersion-modified alloy compositions.

The grain sizes and shapes influence the above-mentioned and other mechanical properties of products of the invention in the manner herein described.

It will be noted that many of the characteristics of the novel products of this invention are developed after the rolling but before the final recrystallization step. In view of this fact, it is possible to take advantage of these characteristics in various metal-forming operations before the final annealing or recrystallization. For instance, applications requiring severe forming, bending, crimping and so on can be performed after heating the rolled ma- 1 terial to temperatures approximating those used during rolling operations. As-rolled sheet ductilities at 1300 F. of approximately 80 to 100% elongation and 0.5 to It bend radii are common for Ni-20 Cr-2 thoria products of the invention which have not been recrystallized.

The products of this invention have high utility by reason of their above-mentioned properties. For instance, they are particularly well suited for use in making turbine engine parts for operation at very high temperature and in oxidizing atmospheres typical of the combustion gas com-positions generated by burning hydrocarbon fuels.

The invention will be better understood by reference to the following illustrative example:

Example 1 A Ni-20 Cr-2 Th0 powder was prepared by coprecipitating NiCO -Cr(OH) -ThO filtering, washing, and drying at 300 C. One hundred parts of this powder were blended with 12 parts of carbon, the blend heated in hydrogen at 400 C. to reduce the nickel oxide, and

6 then at 925 C. in H -CH mixture to reduce the Cr O Excess carbon was removed by heating in hydrogen at 875 C. The particle size of the thoria in the powder was about 16 m The powder was hydrostatically compacted at 60,000 p.s.i., and the compacted billet was machined without lubricants to appoximately 7%" in diameter x 11 /2" long and canned in a cylindrical mild steel can (%3" wall thickness). Mild steel end plates /8" thick) fitted with A" OD. x .022 wall stainless steel tubing were welded in place to seal the can (excepting for the entrance and exit tubing lines in the end plates).

The canned billet was sintered in flowing dry hydrogen, holding the billet temperature successively at 400, 600, 850, and 1750 F. to achieve an exit gas dew point 70 F. Following the final dry hydrogen sinter, the billet was cooled from 1750 F. to room temperature under flowing argon. After cooling the assembly was evacuated, and the gas tubes were sealed by fusion welding.

The sealed billet was placed in a 1750 F. furnace in air. When a billet temperature of 1750" F. was attained, the assembly was extruded to a nominal 1" x 6 sheet bar section. The resulting mild steel jacketed nickelchrome-thoria sheet bar was essentially dense.

The grain size of the as-extruded sheet bar Was approximately 0.5n (nearly eqi-axed). The Rockwell C hardness of the sheet bar was 38. Chemical analyses of the asextruded sheet bar indicated it to contain:

T particle diameter (by extraction and BET.

surface area) =16m,u.

The extrusion piece was sandblasted and cut to yield three 1 x 6" x 14" sheet bars.

Each sheet bar was heated to 1800 F. and rolled on a 2-high mill to a A" x 14" x 24" plate in 10 passes without use of reheats. The mild steel jackets were removed from the plates by pickling and disc sanding. Edge cracks were removed from the plates by mechanical sawing. Each plate was re-canned using mild steel plate on each side and A thick x /2 wide mild steel edge borders. The packages were sealed by fusion welding. Rolling to final gauge was carried out on the 2-high mill after heating each assembly to 1300 F. Re-heating to 1300 F. was used after (1) each, (2) every other, and (3) every 4th roll pass. A final niekel-chrome-thoria sheet gage of .060" was attained in each case. The nickelchrome-thoria sheets were removed from the mild steel cans by hand after shearing of the periphery of the package. The sheets contained small elongated grains -0.25p. in thickness. No recrystallization was found in any of the sheets by light microscopic examination. The Rockwell C hardness of the sheets was 42.

The three sheets were recrystallized by insertion into a 2200 F. furnace. After a 1-hour, 2200 F. heat treatment (in air), the sheets were cooled to room temperature in air.

The recrystallized sheets were lightly sandblasted to remove surface oxides, stretched about to flatten, and sanded to yield 25 RMS, .060"-3.005" products. The sheets were sheared to size and sampled.

Mechanical property testing of each of the three sheets resulted in the following (longitudinal and transverse values):

(1) 2000 F. ultimate tensile strength.

(2) 2000 F. percent elongation (1").

17,400 to 19,100 psi.

ljt,388,010

7 (4) Room temp. 0.2% 90,700 to 101.800 psi.

yield strength.

texture as determined by mechanical hardness impression shape and by conventional pole figure determinations.

Chemical analyses on the three .060" sheets indicated:

ThO (percent by wt.) 1.6, 2.6. 3.6 C, p.p.m. 34, 57, 62 N, ppm. Z3, 41, 58 H, ppm. til, 1, l S, p.p.m. 17, 20, 16, 18, 32, 23

It was observed by bend tests that the warm bend ductility of the sheets of Example 1 was excellent in the "as rolled condition, and hence fabrication was advantageously efiected on this sheet prior to final recrystallization. Temperatures of 1300 F. were optimum for forming this sheet. Forming temperatures as high as t700 F. often cause recrystallization with resultant loss of bend ductility.

We claim:

1. In a process for producing a dispersion-hardened metal sheet having high room temperature ductility and excellent elevated temperature strength and oxidation resistance, in which a powder comprising nickel and from to chromium by weight, said metals having pervasively dispersed therein particles of a refractory metal oxide having a free energy of formation at t000 C. greater than 100 kilocalories per gram atom of oxygen, said particles having an average size less than about 80 millimicrons and being present in the proportion of 0.1 to 6% by volume in the metals, is consolidated to plate form at a temperature below about 2200 F., the steps comprising 1) rolling said plate predominantly in one direction at a temperature of about from 800 F. to 100 F. below its recrystallization temperature, said rolling being sutficient to elfect at least a 50% reduction in the thickness of the plate, and (2) thereafter heating said rolled product to a temperature and for a time sufiicient to totally recrystallize the metal therein.

2. In a process for producing a dispersion-hardened metal sheet having high room temperature ductility and excellent elevated temperature strength and oxidation resistance, in which a powder comprising nickel and from 10 to 30% chromium by weight, said metals having per- 1 vasively dispersed therein particles of a refractory metal oxide having a free energy of formation at 1000 C. greater than 100 kilocalories per gram atom of oxygen and said particles having an average size less than about 80 millimicrons and being present in the proportion of 0.1 to 6% by volume in the metals, is consolidated to plate form at a temperature below about 2200 F, the steps comprising (1) rolling said plate predominantly in one direction at a temperature of about from 800 F. to 100 F. below its recrystallization temperature until its grain structure is characterized by the presence of elongated grains having a length-to-thickness ratio greater than 2, and (2) thereafter recrystallizing said rolled product.

3. In a process for producing a dispersion-hardened metal sheet having high room temperature ductility and excellent elevated temperature strength and oxidation resistance, in which a powder consisting essentially of nickel and from 10 to 30%.' chromium by Weight, said metals having pervasively dispersed therein particles of a refractory metal oxide having a free energy of formation at i000 C. greater than 100 kilocalories per gram atom of oxygen, said particles having an average size less than about millimicrons and being present in the proportion of 1 to 4% by volume in the metals, is compacted, sintered, and consolidated at a temperature below about l750 F, the steps comprising (1) rolling the consolidated plate at a temperature of about from 1500 to 1800 F, [2) further rolling the said plate, at least of said rolling being done in one direction and at a temperature of about from 800 F. to 100 F. below its recrystallization temperature, the total reduction in thickness in steps 1 and 2 being at least 50% of the thickness of the starting plate, and the reduction in step 2 being at least 10% based on the starting step 2 gauge, said rolling producing a metallographic structure which is substantially in the form of elongated grains, having a length-to-thickness ratio greater than 2, and (3) thereafter recrystallizing said rolled product by heating it above its recrystallization temperature.

4. In a process for producing a dispersion-hardened metal sheet having high room temperature ductility and excellent elevated temperature strength and oxidation resistance, in which a powder comprising nickel and from 10 to 30% chromium by weight, said metals having per vasively dispersed therein particles of a refractory metal oxide having a free energy of :formation at 1000 C. greater than 100 kilocalories per gram atom of oxygen, said particles having an average size less than about millimicrons and being present in the proportion of 0.1 to 6% by volume in the metals, is consolidated to plate form at a temperature below about 2200 F. the steps comprising (1) rolling said plate, at least 75% of said rolling being done in one direction and at a temperature of about from 800 F. to F. below its recrystallization temperature, said rolling being sufiicient to effect at least a 50% reduction in the thickness of the plate, (2) forming the rolled product to a desired shape, and (3) thereafter heating the formed product to a temperature and for a time :sufiicient to totally recrystallize the metal therein.

5. In a process for producing a dispersion-hardened metal sheet having high room temperature ductility and excellent elevated temperature strength and oxidation resistance. in which a powder consisting essentially of nickel and about 20% chromium by weight, said metals having pervasively dispersed therein about 2% by volume of thoria particles having an average size in the range of about from 10 to 25 millimicrons is consolidated to plate form at a temperature below about 2200 F., the steps comprising (1) rolling said plate, at least 75% of said rolling being in one direction and at a temperature of from 1100 to 1800 F., said rolling being sufficient to effect at least a 50% reduction in the thickness of the plate, and (2) thereafter heating said rolled product to 2200 F. until the metal therein has totally recrystallized.

6. A dispersion-hardened nickel-chromium sheet comprising nickel and about from 10 to 30% by weight of chromium, said metal having pervasively dispersed there- 2 and a grain thickness in the range of about from to 200 microns.

7. A dispersion-hardened nickehchromium heet comprising nickel and about from 10 to 30% by Weight of chromium, said metal having pervasively dispersed therein about from 0.1 to 6% by volume of particles or" a refractory metal oxide having a free energy of formation at 10GO C. greater than about 106 kilocalories per gram atom of oxygen and an average particle size less than about 80 millimicrons, said product being in the form of sheet characterized by excellent room temperature ductility and high temperature strength and oxidation resistance, and by having a grain structure characterized by the presence of a substantial proportion of grains with a length-to-thickness ratio greater than about 2 and a grain thickness in the range of about from to 60 microns.

3. A dispersion-hardened nickel-chromium sheet comprising nickel and about from 10 to 30% by Weight of chromium, said metal having pervasively dispersed therein about from 0.1 to 6% by volume of particles of a refractory metal oxide having a free energy of formation at 1000 C. greater than about 100 kilocalories per gram atom of oxygen and an average particle size less than about 80 millimicrons, said product being in the form of sheet characterized by excellent room temperature ductility and high temperature strength and oxidation resistance, and by having a grain structure with a cubically aligned preferred orientation, said orientation being described with Miller indicies as (100) 0O1 and a substantial proportion of the grains of the struc ttu'e having a length-to-thickness ratio greater than about 2 and a thickness in the range of about from 15 to 209 microns.

9. A dispersion-hardened nickel-chromium sheet consisting essentially of about from 15 to by weight of chromium, said metal having pervasively dispersed therein about from 1 to 4% by volume of particles of a refractory metal oxide having a free energy of formation at 1000 C. greater than about 106 kilocalories per gram atom of oxygen and an average particle size less than about millimicrons, said product being in the form of sheet characterized by excellent room temperature bend ductility and high temperature strength and oxidation resistance, and by having a grain structure with a cubically aligned preferred orientation, said orientation being described with Miller indicies as (100) Oi)1 and a substantial proportion of the grains of the structure having a length-to-thickness ratio in the range of about 2 to 5 and a thickness in the range of about 15 to 200 microns.

it). A dispersion-modified nickel-chromium sheet consisting essentially of nickel and about 20% by Weight of chromium, said metal having pervasively dispersed therein about 1 to 4% by volume of thoria particles having an average particle size in the range of 10 to 40 millimicrons, said product being in the form of sheet characterized by excellent room temperature bend ductility and high temperature strength and oxidation resistance, and by having a grain structure With a cubically aligned preferred orientation, said orientation being described With Miller indicies as (100) 0i)l and a substantial proportion of the grains of the structure having a length-to-thickness ratio in the range of about 2 to 5 and a thickness of about 20 to microns.

References titted UNiTED STATES PATENTS 12/1962 Grant et a1 ca -2226 12/1962 Grant et al. 75-226 

1. IN A PROCESS FOR PRODUCING A DISPERSION-HARDENED METAL SHEET HAVING HIGH ROOM TEMPERATURE DUCTILITY AND EXCELLENT ELEVATED TEMPERATURE STRENGHT AND OXIDATION RESISTANCE, IN WHICH A POWDER COMPRISING NICKEL AND FROM 10 TO 30% CHROMIUM BY WEIGHT, SAID METALS HAVING PERVASIVELY DISPERSED THEREIN PARTICLES OF A REFRACTORY METAL OXIDE HAVING A FREE ENERGY OF FORMATION AT 1000*C. GREATER THAN 100 KILOCALORIES PER GRAM ATOM OF OXYGEN, SAID PARTICLES HAVING AN AVERAGE SIZE LESS THAN ABOUT 80 MILLIMICRONS AND BEING PRESENT IN THE PROPORTION OF 0.1 TO 6% BY VOLUME IN THE METALS, IS CONSOLIDATED TO PLATE FORM AT A TEMPERATURE BELOW ABOUT 2200*F., THE STEPS COMPRISING (1) ROLLING SAID PLATE PREDOMINANTLY IN ONE DIRECTION AT A TEMPERATURE OF ABOUT FROM 800*F. TO 100*F. BELOW ITS RECRYSTALLIZATION TEMPERATURE, SAID ROLLING BEING SUFFICIENT TO EFFECT AT LEAST A 50% REDUCTION IN THE THICKNESS OF THE PLATE, AND (2) THEREAFTER HEATING SAID ROLLED PRODUCT TO A TEMPERATURE AND FOR A TIME SUFFICIENT TO TOTALLY RECRYSTALLIZE THE METAL THEREIN. 